A widely used method of determining light attenuation in a fiber, which attenuation is observed as an Optical Return Loss (hereinafter “ORL”), utilizes an optical time domain reflectometer instrument (hereinafter “OTDR”), and the measurement process is referred to as optical time domain reflectometry (also referred to hereinafter as “OTDR”). While OTDR instruments and the OTDR method have been used for some years, there are often issues relating to the accuracy of measurements made by inexperienced users. The calibration of OTDR instruments is known, as described for example in the 23 page document entitled “Calibration of Optical Time-Domain Reflectometers,” published by the International Electrotechnical Commission (hereinafter “IEC”) and identified by the designation “IEC TC 86/WG4/SWG2 (Bouquain)5” (hereinafter “IEC TC 86”) and dated 28 Jun. 1999, the disclosure of which is incorporated herein by reference in its entirety. The document refers to such parameters as the backscatter parameter K [in units of seconds−1] and the backscatter coefficient C=K×ΔT, where ΔT is the pulse width of an illumination pulse, measured in units of time (e.g., seconds), and C is a pure number. Annex F of the IEC TC 86 discusses OTDR measurements and backscatter theory as applied to a continuous wave (CW) source. The document also describes methods of calibrating the reflectance of a fiber, for example, at Section 8 and Annex E of the document. As is clear from reviewing this document, the process of measuring the properties of an optical fiber is demanding and requires care and precision for a successful outcome.
Optical return loss (ORL) can cause problems in Dense Wave Division Multiplex (DWDM) and other high-speed optical transmission systems used in communication networks. ORL can affect system performance by causing higher Bit Error Rates (BER) at a receiver and by causing transmitter damage if the output power requirements are unstable.
There is a need for OTDR instrumentation and methods that make possible highly accurate measurements on optical fibers under real world conditions even in the hands of inexperienced, or inexpert, users, such as field installers of optical fiber systems.